The neutralizing antibody component of this core imrnunology laboratory will provide support for all three projects of this program. Specifically, we will assess the magnitude, breadth and duration of neutralizing antibodies against homologous and heterologous strains of SIV, HIV-1 and simian-human immunodeficiency virus (SHIV). Assays will be performed in either human CD4+ T cell lines or peripheral blood mononuclear cells (PBMC) as appropriate, and will include a T cell line adapted (TCLA) variant and multiple primary isolates of HIV- l. These assessments will permit a detailed evaluation of neutralizing antibodies generated by modified recombinant VRP vaccine vectors and modified forms of Env as described in Projects I and 2, respectively. They will also be designed to evaluate neutralizing antibodies as a correlate of immunity against experimental SIV challenge in macaques as specified in Project 3. Cellular immune responses elicited in Projects I, 2 and 3, will be assessed in the cellular immunology component of the core. CTL will be measured as will cytokine synthesis using intracellular assays. Further, tetramer staining will used and specific tetramers produced for particular animals.